Exemplary embodiments of the invention relate generally to a heating, ventilation, air conditioning and refrigeration (HVAC&R) system, and more particularly to HVAC&R system including an integrated vapor compression cycle and absorption refrigeration cycle.
Both absorption refrigerators and mechanical vapor compression (or vapor compression) refrigerators generally use a refrigerant with a very low boiling point. In both refrigerators, when this refrigerant evaporates or boils, it takes some heat away with it, providing a cooling effect. However, absorption refrigeration and vapor compression refrigeration differ in the way the refrigerant is changed from a gas back into a liquid to repeat the cycle. A vapor compression refrigerator uses mechanical work, frequently supplied by an electrically-powered compressor, to increase the pressure and the temperature of the gas, and then condenses the hot, high pressure gas back to a liquid by heat exchange with a cool fluid, such as air or water, as in the case of chillers. An absorption refrigerator changes the pressure and temperature of the gas using a different method that needs only a low-power pump. The gas is first absorbed by an absorbing liquid and the liquid mixture is subsequently heated by an external heat source to generate a hot gas at an elevated pressure. The hot gas is then condensed back to a liquid when cooled. The absorption refrigeration provides a system that can be thermally driven by low grade heat which is generally too expensive to convert to electricity or shaft power to directly drive the compressors.
Conventional refrigeration systems, such as in trucks and trailers for example, use shaft power from an internal combustion engine or electricity from a generator driven by the internal combustion engine. In such applications, the thermal energy from the engine's exhaust and coolant is wasted. In other heating, ventilation, air conditioning, and refrigeration (HVAC&R) applications, solar energy has been used to power the refrigeration system. However, photo voltaic systems require additional components, such as power electronics and electricity storage to stabilize their voltage supply, resulting in high system cost. Also, solar thermal has been used to drive conventional absorption chillers. However, the current commercially available absorption chillers require the solar thermal collectors having high temperature lift, resulting in low collection efficiency. Therefore, a system using high efficiency solar thermal collectors, such as flat panel collectors or wasted heat for example, to achieve vapor compression may significantly improve the efficiency of the overall system. Furthermore, a substantially integrated system of an absorption vapor compression and a mechanical vapor compression can have the advantages of both processes.